High unsaturation butyl rubbers

ABSTRACT

Substantially gel-free, high unsaturation copolymers of isoolefin and diolefin and high unsaturation terpolymers of isoolefin, acyclic diene and cyclic diene having a number average molecular weight of at least about 90,000 and a mole percent of unsaturation of at least 5% and the process for preparing said polymers which comprises carrying out the polymerization in a homogeneous phase, introducing to the system either an aluminum halide in a soluble form or a hydrocarbylaluminum dihalide and carrying the reaction out at a temperature of less than about -100° C.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of Ser. No.631,444 filed Nov. 13, 1975 (U.S. Pat. No. 4,031,300) which is acontinuation-in-part application of Ser. No. 457,109, filed Apr. 1,1974, now U.S. Pat. No. 3,928,297 which is a continuation-in-part ofSer. No. 151,038, filed June 8, 1971, now U.S. Pat. No. 3,808,177.

FIELD OF THE INVENTION

Substantially gel-free, high unsaturation copolymers of isobutylene andisoprene and high unsaturation terpolymers of isobutylene, isoprene andcyclopentadiene having a number average molecular weight of at leastabout 90,000 and a mole percent of unsaturation of at least 5% and theprocess for preparing said polymers which comprises carrying out thepolymerization in a homogeneous phase, introducing to the system eitheran aluminum halide in a soluble form or a hydrocarbylaluminum dihalideand carrying the reaction out at a temperature of less than about -100°C.

BACKGROUND OF THE INVENTION

Polymers and copolymers of isobutylene are well known in the art. Inparticular, copolymers of isobutylene with conjugated multiolefins havefound wide acceptance in the rubber field. These polymers are generallytermed in the art "butyl rubber". The preparation of butyl rubber isdescribed in U.S. Pat. No. 2,356,128, which is incorporated herein byreference.

The term "butyl rubber" as employed in the specification is intended toinclude copolymers made from the polymerization of a reaction mixturecomprising an isoolefin having about 4 to 7 carbon atoms, e.g.isobutylene and a conjugated multiolefin having about 4 to 14 carbonatoms, e.g. isoprene. Although these copolymers are said to containabout 0.2 to about 15% combined multiolefin, in practice the butylrubber polymers of commerce contain about 0.6 to about 4.5 wt. % ofmultiolefin; more generally, about 1.0 to about 1.8 wt. %, the remainderof the polymer being comprised of the isoolefin component.

Efforts to prepare isoolefin-multiolefin polymers of high unsaturationhave met with varying degrees of success. Where substantially gel-freepolymers have been prepared containing more than about 5% multiolefin,the polymers have been of low number average molecular weight. This hasbeen true even where these polymers had high viscosity average molecularweights. In general, however, the products formed by prior art processesare either high in gel content or low in number average molecular weightand of little utility.

Multiolefins are known to be molecular weight and catalyst poisons;furthermore, increased unsaturation in the polymer backbone providespotential sites for gelation. Hence, attempts to prepare more highlyunsaturated isoolefinmultiolefin copolymers by prior art methods haveresulted in the formation of either low molecular weight or resinouscrosslinked polymers which have little or no commercial utility aselastomers.

Although some commercial elastomers such as styrene butadiene rubber orEPDM may contain as much as 2 to 9% gel, isobutylene copolymers ofcommerce are substantially gel free. The isobutylene copolymers maycontain as much as 2% gel but preferably contain less than 1%.

There are numerous patents and literature disclosures which generallydisclose polymers and copolymers of isobutylene, the copolymerspurportedly having from about 0.5 to 98% unsaturation. Where the priorart copolymers are high in unsaturation, however, they are either low innumber average molecular weight or resinous.

Japanese Pat. No. JA27416/68 published Nov. 26, 1968 teaches a processfor preparing copolymers of conjugated diene compounds with isobutylenewhich contain "a large amount of conjugated diene compounds" usingcatalysts prepared by reacting (1) mercuric halide, aluminum halide orhydrogen halide, (2) zirconium halide and (3) aluminum metal in thepresence of an aromatic compound, e.g. benzene. These products aredescribed as copolymers which are "rubbery substances when theisobutylene is high and are resinous when the isobutylene content islow". The resinous properties result from gelation and crosslinking ofthe polymer during its preparation. These gelled and crosslinkedproducts have little utility as rubbers. The products of lowerunsaturation, i.e. high isobutylene content rubbers, are of theconventional butyl rubber type.

Japanese Patent JA27417/68 published Nov. 26, 1968 teaches a method forpreparing copolymers of dienes and isoolefins containing about 0.1 toabout 40 wt. %, preferably about 0.5 to 5 wt. % of diene. The polymersare prepared using a catalyst derived from (1) metal oxides of thegeneral formula M_(x) O_(y), wherein M is nickel or cobalt and1<y/x≦1.5, and (2) aluminum halide. Again, the low unsaturation polymersare the conventional butyl rubbers whereas the highly unsaturatedmaterials are either low in number average molecular weight or aregelled polymers.

U.S. Pat. No. 3,466,268 and its parent counterpart, U.S. Pat. No.3,357,960 disclose a butadiene isobutylene copolymer and a process forpreparing said copolymer. The invention disclosed is a method ofimproving butadiene polymers by incorporating in the structure varyingamounts of isobutylene. Preferably, the amount of isobutyleneincorporated is said to be about 2 to 40 wt. %. The polymers disclosedare generally low in number average molecular weight. Substitution ofisoprene for butadiene results in highly crosslinked copolymers whichhave little utility.

U.S. Pat. No. 2,772,255 (Br. 744,514) discloses a method for preparinghigh molecular weight butyl rubbers. In general, the polymers which areprepared are conventional butyl rubbers having less than 3 mole %unsaturation. Attempts to produce butyl rubber type polymers havingunsaturation in excess of 5 mole % unsaturation result in products whicheither are low in number average molecular weight or are gelled andhighly crosslinked.

High unsaturation isobutylene-isoprene copolymers have been prepared(see, for example, U.S. Pat. No. 3,242,147 incorporated herein byreference). Although these polymers are purportedly high in viscosityaverage molecular weight, the number average molecular weights are low.Hence, the products have little commercial significance.

U.S. Pat. No. 2,521,359 to Garber discloses copolymers consistingprimarily of cyclopentadiene with minor amounts of other monomers(including isobutylene) as resins capable of air curing to toughcoatings and films. The copolymers of Garber having more than 50%cyclopentadiene are of extremely low molecular weight.

Unlike plastics, elastomers require a high number average molecularweight in order to realize desirable levels in physical properties. Forexample, tensile strength for elastomers is critically dependent onnumber average molecular weight since these polymers are used well abovetheir glass transition temperature and are generally amorphous.

In contrast to elastomers, plastics are used well below their glasstransition temperature and it is molecular associations which gives themtheir structural integrity. As a result, number average molecularweights in the order of 10,000 to 70,000 are adequate for commercialutility.

Elastomers, on the other hand, obtain their structural integrity from acrosslinked network. Perfection of this network is directly dependent onthe length of the polymer molecules from which the network is derived.Number average molecular weight (Mn) is a measure of the length of themolecules. Viscosity or weight average molecular weights are misleadingmeasurements since their numerical value is greatly affected by smallvariations in the distribution of the higher molecular weight fractions.Hence, polymers of low number average molecular weight may have highviscosity average molecular weight as a result of disproportionatedistribution of the high molecular weight fraction.

The importance of number average molecular weight on tensile strengthhas long been recognized (see, for example, Flory, p. 5, Ind. Eng.Chem., 38, 417 (1946), incorporated herein by reference. Flory showedthat, for low unsaturation elastomeric copolymers of isobutylene,tensile strength increased rapidly as the number average molecularweight was increased beyond a minimum value (i.e. 100,000) thenapproaches an asymptotic limit.

For economic reasons, oil extendability is an essential characteristicof a commercial elastomer for almost all major uses. The tensilestrength of butyl rubber vulcanizates is reduced by the addition of oil,and to retain the original tensile strength of the undiluted compositionit is necessary to increase the number average molecular weight. Oilextension also improves the low temperature properties of butyl innertubes and when this phenomenon was discovered, it was necessary todevelop higher molecular weight polymers to accommodate the added oil.See, for example, Buckley et al, Ind. Eng. Chem., 42, 2407 (1950).

This finding resulted in the rapid adoption by industry of the highmolecular weight type of butyl GR-1-18 with Mooney viscosity greaterthan 71 (212° F.). These materials generally have number averagemolecular weights of 150,000 or greater. In contrast, the previouslyused polymers which have number average molecular weights of less than120,000 with Mooney viscosity specification of 38-49 (212° F.) werelimited to applications which did not require oil extension, and todayrepresent a very minor portion of the butyl rubber market having beensupplanted almost entirely by the higher molecular weight butyl rubbers.

Although it has been postulated that higher unsaturation copolymers ofisobutylene would be attractive polymers, useful polymers have not beenavailable since the prior art methods are not capable of producinghighly unsaturated, e.g., at least 5 mole % to about 45 mole %,isobutylene copolymers of sufficiently high number average molecularweight. Hence, the prior art isobutylene-conjugated diene copolymersoffered commercially are low in unsaturation, e.g., 1-4.5 mole %.

Hence, heretofore, methods of preparing copolymers of isoolefins andconjugated dienes have not included a means for making commercialquality elastomers containing greater than 5 mole % diene.

Although the isobutylene-conjugated dienes of commerce have improvedozone resistance, these polymers are still subject to ozone cleavagesince the site of unsaturation is in the polymer backbone. It has beenpostulated that isobutylene copolymers having unsaturation on the sidechain rather than the backbone would be highly resistant to ozoneattack. Attempts to produce such polymers using cyclopentadiene as thediene comonomer have been notably unsuccessful.

Isobutylene-cyclopentadiene copolymers and terpolymers of the prior arthave been too low in molecular weight to be of commercial significance.Some improvement in molecular weight has been accomplished bycopolymerizing isobutylene with minor amounts of cyclopentadiene (CPD)along with other monomers including crosslinking agents such as divinylbenzene. The resulting products are somewhat improved terpolymers ortetrapolymers resulting from the linking of the low molecular weightisobutylene-CPD chains into two dimensional highly branched polymers.Such polymers, however, have inferior physical properties as compared tothe butyl rubbers of commerce and hence have not gained acceptance.

A review of the art illustrates the problems encountered where attemptswere made to prepare copolymers of isobutylene and cyclopentadiene(CPD). For example, U.S. Pat. No. 2,577,822, incorporated herein byreference, teaches the need for the addition of divinyl benzene in orderto compensate for the deleterious effect of CPD on molecular weight.

U.S. Pat. No. 3,080,337, incorporated herein by reference, teaches theaddition of isoprene as a third monomer but the resulting products arelow in unsaturation and have poor physical properties. Others have madevarious attempts to produce CPD isoolefin copolymers with varyingdegrees of success; see, for example, U.S. Pat. Nos. 3,239,495;3,242,147; 2,521,359; British Pat. No. 1,036,618 and I & EC Prod R andD, 1, 216-20 (1962) incorporated herein by reference. These polymers,however, have substantially no commercial significance because, evenwhen only minor amounts of CPD were present, they are low in numberaverage molecular weight.

SUMMARY OF THE INVENTION

It has surprisingly been found that valuable substantially gel-freecopolymers of isoolefins and isoprene having a mole % unsaturation of atleast about 5% can now be prepared having molecular weight (Mn) of lessthan about 120,000, preferably at least about 90,000, terpolymers ofisoolefins, isoprene and cyclopentadiene having a mole % unsaturation ofat least about 5% can now be prepared having molecular weight (Mn) ofless than about 120,000, preferably at least about 90,000 by carryingout the polymerization in the presence of not more than 40 wt. %, basedon the total of monomers plus cosolvent, of a cosolvent which is asolvent for the polymer at the polymerization temperature and carryingout the reaction at a temperature of less than about -100° C. Thecatalyst may be an aluminum halide introduced into the reaction zonedissolved in a polar solvent or the catalyst may be ahydrocarbylaluminum dihalide as disclosed in U.S. Pat. No. 3,856,763incorporated herein by reference.

The quantity of cosolvent used is kept to a minimum in order to maximizemolecular weight. The optinum cosolvent level is determined by selectingthe minimum solvent-monomer ratio at which the copolymer to be preparedremains in solution at the polymerization temperature.

Surprisingly, the process of this invention makes it possible to prepareisobutylene-isoprene copolymers and isobutylene-isoprene-cyclopentadiene(CPD) terpolymers of the desired number average molecular weight.Terpolymers of isobutylene, CPD and a third conjugated multiolefin haveunusual ozone resistance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. I shows the relationship between critical homogeneouspolymerization temperature and diene content.

FIG. II shows the effect of polymerization temperature on number averagemolecular weight.

FIG. III shows the effect of cosolvent concentration on molecularweight.

FIG. IV shows the effect of polymerization temperature on conversion.

FIG. V shows catalyst efficiency as a function of cosolventconcentration.

FIG. VI shows the relationship between mole % cyclopentadiene in thefeed as compared to mole % cyclopentadiene in the polymer.

FIG. VII shows the relationship between glass transition temperature andmole % cyclopentadiene enchainment in the copolymer.

FIG. VIII is a correlation of D# (vol. % CPD in monomer) with mole %cyclopentadiene in the monomer feed.

DETAILED DESCRIPTION

This invention relates to a method for preparing substantially gel-freecopolymers of isobutylene and isoprene and terpolymers ofisobutylene-isoprene-cyclopentadiene having a number average molecularweight, as measured by membrane osmometry, of at least about 90,000 anda mole % unsaturation of at least about 5%.

In order to obtain the copolymers and terpolymers of this invention, thereaction should be carried out at less than about -100° C. To obtain thedesired number average molecular weight in a substantially gel-freepolymer, a homogeneous polymerization is required. This is achieved bycarrying out the reaction in a vehicle which is a solvent for thecopolymer at the reaction temperature. The vehicle comprisespredominantly the monomers to be polymerized in conjunction with aninert cosolvent or mixtures of inert cosolvents plus catalyst solvent.

The copolymers of the instant invention are formed from an isoolefin anda straight chain conjugated hydrocarbon multiolefin or a cyclicconjugated hydrocarbon multiolefin.

The terpolymers of the instant invention are formed from an isoolefinand two conjugated hydrocarbon multiolefins, wherein the twomultiolefins can either be one straight chain multiolefin and one cyclicmultiolefin or two cyclic multiolefins.

The isoolefins suitable for use in the practice of the inventions arepreferably hydrocarbon monomers having about 4 to about 10 carbon atoms.Illustrative nonlimiting examples of these isoolefins are isobutylene,2-methyl-1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, beta-pinene,etc. Preferably, the isoolefin is isobutylene.

The multiolefins suitable for use in this invention are conjugatedhydrocarbon multiolefins having 5 to about 14 carbon atoms; morepreferably, the multiolefins are conjugated diolefins of 5 to 9 carbonatoms. Illustrative nonlimiting examples of these multiolefins areisoprene, piperylene, 2,3-dimethyl butadiene,2,5-dimethylhexadiene-2,4-ene, cyclopentadiene, cyclohexadiene,methylcyclopentadiene, fulvene, etc and mixtures thereof.

It is essential in carrying out the process of this invention that thecosolvent comprise at least 5% by volume and not more than 40% by volumeof the total reaction mixture. Preferably, about 5 to about 30 volume %solvent is used; more preferably about 7.5 to 25 wt. %, most preferablyabout 10 to about 20 wt. %, e.g. 15 volume %. The term "total reactionmixture" as used in the specification and claims means total monomersplus cosolvent.

The optimum amount of cosolvent to be used is the minimum amountnecessary to avoid reactor fouling or gelation. If too little cosolventis used reactor fouling or gelation of the product results. Too high alevel results in undesirable lowering of number average molecularweight.

For the purposes of this invention, it is convenient to define thevolume % of inert cosolvent as that calculated based on the volume ofmonomers at -78° C. (dry ice temperature) while the volume of cosolventis determined at 25° C. The volume % of cosolvent as calculated isuncorrected for volume changes and cooling of the solvent to reactionconditions.

The minimum quantity of a given cosolvent required to produce gel-freepolymers is a function of the cosolvent, the conjugated multiolefin usedand the polymerization temperature. Having selected the composition ofthe blend of monomers and the cosolvent to be used the minimum quantityof cosolvent required is readily determined by carrying out thepolymerization using varying amounts of cosolvent. The minimum quantityof cosolvent necessary is that amount required to maintain a homogeneoussystem; that is to prevent precipitation of polymer duringpolymerization.

The term "cosolvent" as used in the specification and claims means theinert solvent which, together with the monomer feed, comprises thevehicle for the reaction. The cosolvent and monomers must be mutuallysoluble and the blend of monomers plus cosolvent must be a solvent forthe copolymer at the polymerization temperature. The term "inert" meansthat the cosolvent will not react with the catalyst or otherwise enterinto the polymerization reaction. The cosolvent must not containsubstituents in its molecule which will interfere with thepolymerization reaction. Aliphatic hydrocarbons are suitable cosolvents.The preferred cosolvents are paraffinic hydrocarbons, and carbondisulfide. Preferably, the paraffinic hydrocarbon solvent is a C₅ -C₁₀hydrocarbon, more preferably a C₅ to C₈ hydrocarbon. Illustrativeexamples of the hydrocarbon solvents are pentane, isopentane,methylpentane, hexane, cyclohexane, methylcyclohexane,dimethylcyclohexane, heptane, isooctane, 1,2,3,3-tetramethyl hexane,tetramethyl cyclohexane, etc. Generally any paraffin, whether normal,branched or cyclic which is a liquid polymerization conditions, may beused. The term "paraffin" as used in the specification and claimsincludes normal paraffins, cycloparaffins and branched paraffins ormixtures thereof. When the diene is a cyclodiene preferred cosolventscontain cycloparaffins.

Since the monomers act as part of the solvent system for the polymer,the conversion level of the polymerization must not be so great as toresult in precipitation of the copolymer as a result of depletion ofsolvent. Preferably the conversion level is about 2 to about 30%; morepreferably about 3 to 15%; most preferably about 5 to about 13%, e.g.,10%.

In the practice of this invention the catalyst can be an aluminum halideor hydrocarbylaluminum dihalide. Where an aluminum halide is used, itmust be in the form of a homogeneous solution or submicron dispersion ofcatalyst particles, e.g., colloidal dispersion. Therefore, the aluminumhalide catalyst must be dispersed or dissolved in a suitable catalystsolvent or mixture of solvents. The aluminum halide catalyst solventmust be a polar solvent. Illustrative examples of suitable aluminumhalides are AlCl₃ and AlBr₃. The preferred aluminum halide catalyst isaluminum chloride. The term "polar solvent" as used in the specificationand claims means non-aromatic, organic solvents having a dielectricconstant at 25° C. of at least 4, preferably about 4 to about 20, morepreferably about 6 to about 17; most preferably about 9 to about 13.These polar solvents, however, must not contain sulfur, oxygen,phosphorus or nitrogen in the molecule since compounds containing theseelements will react with or otherwise deactivate the catalyst.

The preferred polar solvents are inert halogenated aliphatichydrocarbons; more preferably halogenated paraffinic hydrocarbons andvinyl or vinylidene halides; most preferably primary or secondarychlorinated paraffinic hydrocarbons. The halogenated hydrocarbon ispreferably a C₁ -C₅ paraffin hydrocarbon; more preferably a C₁ -C₂paraffin. The ratio of atoms to halogen atoms in the polar solvent ispreferably 5 or less. Preferably the halogen is chlorine.

Illustrative examples of these polar organic solvents aremethylchloride, ethyl chloride, propyl chloride, methyl bromide, ethylbromide, chloroform, methylene chloride, vinyl chloride, vinylidenechloride, dichloroethylene, etc. Preferably, the polar solvent is methylchloride or ethyl chloride. Generally any inert halogenated organiccompound which is normally liquid under polymerization conditions andhas a dielectric constant of at least 4.0 may be used.

It is essential in carrying out this invention that the aluminum halidecatalyst be in solution in the polar organic solvent prior tointroduction of the catalyst to reaction medium. Combining the polarorganic solvent with the reaction medium and thereafter adding thealuminum halide catalyst thereto will not result in the production ofthe high Mn, high unsaturation polymers of this invention.

Use of the term "solution" with reference to the polar organicsolvent/aluminum halide systems is intended to include both truesolutions and colloidal dispersions since they may exist concurrently inthe same system.

The aluminum halide/polar solvent catalyst preferably comprises about0.01 to about 2 wt. % aluminum halide; more preferably about 0.05 toabout 1; most preferably 0.1 to about 0.8.

As previously noted, the catalyst may also be a hydrocarbylaluminumdihalide. The hydrocarbyl group can be a C₁ -C₁₈ straight chain,branched or cyclic group. Both cycloaliphatic and aromatic substituentscan comprise the hydrocarbyl radical. Alkyl groups, especially loweralkyl groups, e.g., C₁ -C₄, are preferred because of their generalavailability and economy of use. The halide can be bromine or chlorine,preferably chlorine. The term "dihalide" as used in the specificationand claims means dichloride or dibromide.

Illustrative examples of these hydrocarbyl aluminum dihalides aremethylaluminum dichloride, ethylaluminum dichloride, isobutylaluminumdichloride, methylaluminum dibromide, ethylaluminum dibromide,benzylaluminum dichloride, phenylaluminum dichloride, xylylaluminumdichloride, toluylaluminum dichloride, butylaluminum dichloride,hexylaluminum dichloride, octylaluminum dichloride, cyclohexylaluminumdichloride, etc. The preferred catalysts are methylaluminum dichloride,ethylaluminum dichloride and isobutylaluminum dichloride.

The hydrocarbyl aluminum dihalide catalyst may be added neat or insolution. Preferably where a catalyst solvent is used, it is a liquidparaffin solvent or cycloparaffin solvent. It is advantageous though notnecessary to use paraffins at low freezing point. Methylcyclohexane isparticularly useful since catalyst solutions of about 1% concentrationdo not freeze at -120° C.

The concentration of the catalyst is not critical. Very dilute catalystsolutions, however, are not desirable since substantial fractions of thecatalyst may be deactivated by impurities. Very concentrated solutionsare undesirable since at polymerization temperatures catalyst may belost by freezing out of solution.

In carrying out the polymerization of this invention those skilled inthe art will be aware that only catalytic amounts of catalyst solutionare required. Preferably the volume ratio of monomer plus cosolvent tocatalyst solution is about 100/1 to about 9/1; more preferably about80/1 to about 10/1; most preferably about 50/1 to about 20/1.

In practicing the process of this invention, it is essential that thepolymerization be carried out in the homogeneous phase without theprecipitation of polymer. Conventional slurry processes are inapplicablefor the preparation of the high unsaturation polymers of this inventionsince by their nature they result in polymer precipitation with gelationof the polymer as a consequence.

The amount of cosolvent required in order to maintain the polymerizationreactants and product in solution throughout the polymerization is afunction of the multiolefin selected for polymerization and itsconcentration in the monomer feed. The polymerization temperature atwhich precipitation of polymer will occur is itself a function of theamount of and type of cosolvent and the particular multiolefin beingcopolymerized.

The term "critical homogeneous polymerization temperature" are used inthe specification and claims means that polymerization temperature belowwhich precipitation of polymer will occur when no cosolvent is includedin the reaction mixture, i.e., the only solvent for the reactants andproduct being the monomer feed.

Characterization of polymers prepared by bulk polymerization, i.e.,without cosolvent, shows that the polymers formed are low in numberaverage molecular weight (Mn). In order to increase Mn, the lowering ofpolymerization temperature is an obvious expedient. However, in theabsence of cosolvent, the result is not greater Mn but gelation.

The problem of gelation is obviated by the addition of a cosolvent whichpermits the lowering of polymerization temperature below the criticalhomogeneous polymerization temperature. It has been found that apolymerization temperature below about -100° C. is necessary in order toachieve Mn values of at least 90,000 for the copolymer and terpolymersof the present invention. At least 5 volume % inert solvent based on themonomer feed is necessary in order to carry out the polymerization insolution at these low temperatures.

Referring now to FIG. I, the volume % of multiolefin (isoprene) in themonomer blend (B#) is plotted as a function of the polymerizationtemperature below which precipitation of polymer and as a consequencegelation occurs in the absence of cosolvent. The curve represents thecritical homogeneous polymerization temperatures forisobutylene-isoprene systems.

The process of this invention incorporates the isobutylene and isopreneinto the copolymer in substantially the same ratio as it exists in thefeed. For example, where an isobutylene-isoprene monomer feed comprises15 volume % isoprene the polymer formed therefrom comprises about 12.5mole % unsaturation. Characterization of polymers prepared by bulkpolymerization, i.e., without cosolvent, shows that the polymers formedare low in number average molecular weight (Mn). In order to increaseMn, the lowering of polymerization temperature is an obvious expedient.However, in the absence of cosolvent, the result is not greater Mn butgelation.

The term "unsaturation" or "multiolefin content" as used with referenceto the amount of multiolefin enchainment in the product are equivalentterms. The composition of the copolymer (mole % unsaturation=mole %diene content) is substantially the same as the composition of the feedfor acyclic dienes such as isoprene and piperylene. However, where thediene is a cyclic diene such as cyclopentadiene, it is present inconsiderably higher amounts, e.g., 3 to 4 times, in the copolymer as inthe feed.

The necessity for utilizing low polymerization temperatures isexemplified by FIG. II which shows the exponential decrease in numberaverage molecular weight with increasing temperature. The criticality ofselecting the proper quantity of cosolvent is demonstrated in FIG. III.Too little cosolvent results in precipitation of the polymer withreactor fouling or gelation. Too much cosolvent results in a lowmolecular weight product. Further benefits of low temperature and properselection of appropriately low cosolvent concentration are demonstratedin FIGS. IV and V. FIG. IV shows that reactivity is favored by lowtemperatures (in addition to the molecular weight benefit). FIG. V showsthat catalyst efficiency is favored by low cosolvent concentration (inaddition to the molecular weight benefit).

In practicing the process of this invention, one skilled in the art mayproceed as follows in order to determine the preferred reactionconditions.

First, a convenient polymerization temperature below about -100° C. isselected. Next the desired feed composition, i.e. monomers and ratio ofisoolefin to conjugated dienes and the cosolvent to be used areselected. Polymerization reactions are carried out using successivelygreater amounts of solvent. The initial polymerization reaction iscarried out using 5 volume % based on the total of monomer plus solventof the cosolvent since lesser amounts will be inadequate. In eachsuccessive run an additional 5 volume % is added. The procedure iscontinued until the reaction medium remains clear throughout thereaction. Turbidity is indicative of precipitation of polymer whichleads to reactor fouling or gelation.

The polymer formed is characterized for Mn and mole % unsaturation.Where a higher Mn is desired it may be achieved by either lowering thepolymerization temperature or where possible using slightly less solventthan determined by the above method, e.g., 1-2 vol. % less, providedthat turbidity does not occur. Reduction of polymerization temperaturemay result in a greater cosolvent requirement. Hence, the aforegoingprocedure of adding additional solvent to the reaction medium must becontinued until the reaction medium is again clear throughout thepolymerization.

Where the mole % unsaturation is to be adjusted somewhat more or less ofthe diene is used depending on whether a slightly higher or lowerunsaturation is desired. Change in feed composition may requirereadjusting the cosolvent requirement. Generally, increasing themultiolefin content of the monomer feed decreases the cosolventrequirements of the system with acyclic diene-like isoprene andincreases the cosolvent requirement with cyclicdiene such ascyclopentadiene.

The optimum reaction conditions are those which give the maximum Mn atthe highest (warmest) temperature for the desired unsaturation level.The smaller the quantity of cosolvent used the greater the Mn. Economicconsiderations dictate the use of the warmest temperature practical forpolymerization. Use of lower temperatures will necessitate the use ofgreater amounts of cosolvent. Preferably the polymerization temperatureis above -110° C.

In an alternate approach to determine the necessary quantity ofcosolvent, the reactions are carried out in bulk without usingcosolvent. For each different multiolefin content monomer feed,polymerizations are carried out at progressively lower temperaturesuntil the critical homogeneous polymerization temperature for the feedcomposition is determined. The polymerization is repeated for differentfeed compositions and the data obtained are the critical homogeneouspolymerization temperatures as a function of multiolefin content of thefeed. A plot of these data gives the critical homogeneous polymerizationtemperature curve analogous to that of FIG. I. The polymer formed isanalyzed for multiolefin content and a determination is made of thecorrelation mole % unsaturation in the polymer and volume % multiolefinin the feed. The polymers formed in bulk copolymerization of isobutyleneand isoprene or isobutylene-isoprene-cyclopentadiene are unsuitable forcommercial use since they have a very low Mn. In order to increase theMn of the polymer it is necessary to carry out the polymerization atlower temperatures, e.g., less than about -100° C. which requires theaddition of cosolvent to prevent precipitation of polymer duringpolymerization.

The quantity of solvent used should be kept to a minimum since excesscosolvent results in the lowering of Mn. In determining the amount ofsolvent to be used the monomer feed composition is determined. Aconvenient polymerization temperature below about -100° C. is selected.

The minimum cosolvent requirements for a particularisoolefin-multiolefin may be determined by carrying out thepolymerization at the critical homogeneous polymerization temperaturefor the isoolefin-multiolefin feed composition, terminating thepolymerization by destroying the catalyst and, with constant stirring,lowering the temperature of the system to the desired polymerizationtemperature. The polymer which, of course, is by definition insolublebelow the critical homogeneous polymerization temperature willprecipitate out and the system will appear turbid. The polymer will notbe gelled, however, since polymerization was terminated prior toprecipitation. The cosolvent selected is then added in incrementalamounts until the turbidity disappears. The quantity of solvent so addedis a good approximation of the minimum solvent requirements for a givenisoolefin-multiolefin feed to be polymerized at a given temperature.

The term "solution polymerization" as used in the specification andclaims means a polymerization carried out so that the polymer productremains dissolved throughout the reaction.

Where the diene to be polymerized is isoprene, the preferred cosolventsare hexane(s), heptane(s), cyclohexane, and methylcyclohexane ormixtures thereof utilized at about 5 to about 30 volume %; morepreferably at about 10 to about 25 volume %, e.g., 10 volume %. Wherethe diene is cyclopentadiene the preferred cosolvents aremethylcyclohexane (MCH) and cyclohexane or paraffin mixtures containingone of these materials utilized at about 10 to about 30 volume %, e.g.,20 to about 25 volume %.

The products of this invention offer a number of important advantagesover the commercially available butyl rubbers. In addition to possessingsuperior cold flow and green strength properties while retaining the lowair permeability and mechanical damping characteristics of conventionallow unsaturation isoolefin copolymers, the products of this inventionoffer greater versatility in vulcanization techniques. Furthermore whilethe vulcanization of conventional isoolefin-multiolefin copolymersrequires the use of ultra-accelerator type cures, e.g., thiuram (Tuads)or dithiocarbamates (Tellurac), the products of this invention may bevulcanized using the thiazole, e.g., mercaptobenzothiazole, type curescurrently used in the vulcanization of general purpose rubbers, e.g.,natural rubber, SBR, polybutadiene, etc. Because of certain factors ofwhich premature vulcanization (scorch) is a prime example, modernpractice has tended towards the use of a special class of thiazolescalled delayed action accelerators. These delayed action acceleratorspermit the processing of the compounded rubber (including vulcanizingagents) at the vulcanization temperature for a predetermined period oftime before vulcanization commences. Such cure techniques are notpossible with conventional isoolefin copolymers. The delayed actionaccelerators are, however, used advantageously in the vulcanization ofthe isoolefin copolymers of this invention.

The delayed action accelerators suitable for use in vulcanizing theproducts of this invention include the benzathiole sulfenamides havingthe general formula: ##STR1## wherein X is an amino group. The aminogroup is mono or diorganosubstituted and may be cyclic includingheterocyclic. For example, X may be ##STR2## or --N═R₂ where R₁ is H orR, R is organo or cycloorgano, and R₂ is a divalent organo radical.Illustrative examples of X are cyclohexylamino, tertiary butyl amino,diisopropyl amino, dicyclohexyl amino, pentamethylene-amino, morpholino,2-(2,6-dimethyl morpholino) etc. Specific illustrative examples of thesesulfenamides are N,N-diethylbenzothiazole-2-sulfenamide, N-N-diisopropylbenzothiazole-2-sulfenamide, N-tertiary butylbenzothiazole-2-sulfenamide, N-cyclohexyl benzothiazole-2-sulfenamide,N,N-dicyclohexyl benzothiazole-2-sulfenamide, 2-(morpholino)benzothiazole sulfenamide, 2-(2,6-dimethyl morpholino) benzothiazolesulfenamide, 2-piperdinyl benzothiazole sulfenamide. In general, anybenzothiazole sulfenamide may be used as a delayed action acceleratorfor the sulfur vulcanization of the polymers of this invention.

The delayed action accelerator is incorporated into the vulcanizablepolymer composition at preferably about 0.1 to about 5 wt. % based onthe polymer; more preferably about 0.25 to about 3.5; most preferablyabout 0.5 to about 3.0 wt. %, e.g., 0.5 to about 2.5 wt. %.

As it is well known, the delayed action cures are sulfur cures andsulfur must be incorporated into the polymer blend either as elementalsulfur or as nonelemental sulfur. Suitable nonelemental sulfur is in theform of those compounds which will release sulfur to the polymer undervulcanization conditions. For a description of these nonelemental sulfurcompounds, generally, see Vulcanization of Elastomers, Ch. 4, J. C.Ambelang, Reinhold, New York, 1964. Illustrative examples of thesenonelemental sulfur compounds are dimorpholvinyl disulfide and alkylphenol disulfides. The term "sulfur donor" as used hereinafter in thespecification and claims means elementsl sulfur as well as theaforementioned nonelemental sulfur compounds. The quantity of sulfurdonor required for vulcanization is well known. Where the sulfur donoris elemental sulfur, it is incorporated into the polymer at about 0.1 toabout 5 wt. % based on the polymer; more preferably about 0.25 to about3.5 wt. %; most preferably about 0.5 to about 3.0 wt. %, e.g., 0.5 toabout 2.5 wt. %. Where the sulfur donor is a nonelemental sulfurcompound, it is incorporated at a weight % of about three times thatrequired for elemental sulfur. The term "nonelemental sulfur compounds"means organic compounds containing sulfur and capable of donating thesulfur to a vulcanization reaction, e.g., disulfides and polysulfides.

The delayed action accelerators may be modified by retarders andactivators which will respectively retard or activate the sulfurvulcanization. The addition of the retarder will further delay the timeat which vulcanization occurs while the activator will causevulcanization to occur sooner, e.g., shorter delay time.

The retarders suitable for use in the practice of this invention includeorganic compounds having a pKa of about 2 to less than 7; preferablyabout 3 to about 6.5; more preferably about 4 to about 6, e.g., 5. Theterm pKa is the dissociation constant as measured in aprotic solvents,see for example Acid-Base Behavior in Aprotic Solvents NBS Monograph105, August 1968.

The activators suitable for use in the practice of this invention aremetallic oxides, hydroxides and alkoxides of Group Ia and Group IIametals of the Periodic Table of the Elements and organic compoundshaving a pKa of about 8 to about 14; preferably about 9 to about 12;more preferably about 9.5 to about 11, e.g., 10.

Illustrative examples of retarders are N-nitroso diphenylamine,N-cyclohexyl thiophthalimide, phthalic anhydride, salicylic acid,benzoic acid, etc. Generally, the preferred retarders are nitrosocompounds, phthalimides, anhydrides and acids.

Illustrative examples of activators are MgO, diphenylquanidine,hexane-1-amine, 1,6-hexane diamine, sodium methoxide, etc. The preferredactivators are quanidines and amines.

The retarders and activators are preferably incorporated into thepolymer at about 0.1 to about 5 wt. %; more preferably about 0.25 toabout 3.5 wt. %; most preferably about 0.5 to about 3.0 wt. %, e.g., 0.5to about 2.5 wt. %. As it is well known in the elastomeric art, thecopolymers and terpolymers of the instant invention can be readilyextended with fillers and oils for further modification of the physicalproperties of the resultant articles of commerce.

The copolymers and terpolymers of the instant invention can be readilyblended with other rubbers for modification of physical and chemicalproperties by techniques well known in the art. These other rubbers areselected from the group consisting of non-polar crystallizable rubbers(i.e. crystallization either deduced by low temperature or strain or amixture thereof), polar crystallizable rubbers, non-polarnon-crystallizable rubbers, and polar non-crystallizable rubbers. Theserubbers are contained in the blend compositions at a concentration levelof about 5 to about 95 parts by weight per 100 parts of the total of therubber plus copolymer and/or terpolymer, more preferably about 10 toabout 50 and most preferably about 10 to about 30. Typical, butnon-limiting examples of each class are: non-polar crystallizablerubbers, natural rubber, low isoprene butyl rubbers having less than 1.0mole percent isoprene; polar crystallizable rubbers-polychloroprenerubbers (i.e., the neoprene types), non-polar non-crystallizablerubbers-styrene butadiene copolymers, polybutadienes and butyl rubberscontaining more than 1.0 mole percent isoprene; and polarnon-crystallizable rubbers-styrene acrylonitrile copolymers.

The fillers employed in the present invention are selected from thegroup consisting of carbon blacks, silica, talcs, ground calciumcarbonate, water precipitated calcium carbonate, or delaminated,calcined or hydrated clays and mixtures thereof. These fillers areincorporated into the blend composition at about 5 to about 350 parts byweight per hundred parts of polymer, more preferably at about 25 toabout 350; and most preferably at about 50 to about 300. Typically,these fillers have a particle size of about 0.03 to about 20 microns,more preferably about 0.3 to about 10, and most preferably about 0.5 toabout 10. The oil absorption as measured by grams of oil absorbed by 100grams of filler is about 10 to about 100, more preferably about 10 toabout 85 and most preferably about 10 to about 75.

The compounding and plasticizer oils employed in the present inventionare non-polar process oils having less than about 2 wt. % polar typecompounds as measured by molecular type clay gel analysis. These oilsare selected from paraffinics ASTM Type 104B as defined inASTM-D-2226-70, aromatics ASTM Type 102 or naphthenics ASTM Type 104A,wherein the oil has a flash point by the Cleveland open cup of at least350° F., a pour point of less than 40° F., a viscosity of about 70 toabout 3000 S.S.U.'s at 100° F. and a number average molecular weight ofabout 300 to about 1000, and more preferably about 300 to 750. Thepreferred process oils are paraffinics.

The oils are incorporated into the blend composition at a concentrationlevel of about 5 to about 200 parts by weight per hundred parts ofpolymer; more preferably at about 25 to about 150, and most preferablyat about 50 to about 150.

Other plasticizers suitable for use in the present invention are mediumviscosity ester plasticizers for special high efficiency in increasingresilience particularly at low temperature. Some examples, which are notintended to be limiting in scope are dioctyl phthalate, dioctyl azelate,dioctyl sebacate or dibutyl phthalate. The ester plasticizer isincorporated into the blend composition at a concentration level ofabout 5 to about 100 parts by weight per hundred of polymer, morepreferably about 5 to about 75, and most preferably about 5 to about 50.

Terpolymers of isoolefins and cyclodienes, e.g., isobutylene-isopreneand cyclopentadiene possess markedly improved resistance to degradationby ozone over the acyclic diene copolymers. Although it has beenpostulated that such terpolymers would have such improved properties asa result of having the unsaturation located in a side chain rather thanin the backbone, it has heretofore not been possible to preparesubstantially gel-free isoolefin-cyclodiene terpolymers of high numberaverage molecular weight even at low levels of unsaturation.

Utilizing the process of this invention, it is now possible to preparesuch cyclodiene terpolymers having as little as 0.5 mole % unsaturationand as high as 45 mole % unsaturation. Preferably, the polymers containabout 5% to about 45%; more preferably about 5 to about 40 mole %unsaturation; still more preferably about 8 to about 40; and mostpreferably about 8 to about 30 mole %, e.g., about 12 to about 30 mole%.

As a result of the relatively lower reactivity of the unsaturation ascompared to the isoprene copolymers, copolymers having incorporatedtherein about 2-4 mole % cyclopentadiene are about as reactive as butylrubber having an isoprene content of about 0.5 to about 1.5 mole % andrequire ultra acceleration for sulfur vulcanization. By contrast thehigher unsaturation copolymers, e.g., at least 5 mole %, preferably atleast 8 mole %, may be sulfur vulcanized using the delayed actionaccelerator cure systems described above.

In general, the copolymers of this invention must not contain more thanabout 45 mole % unsaturation. Above about 45 mole % unsaturation,polymers prepared from acyclic multiolefins are intractable andunstable, e.g., gel on standing. Where the multiolefin is a cyclicmultiolefin above 45 mole % unsaturation, the glass transitiontemperature of the polymer is too high. As a result, the polymers havepoor low temperature characteristics. Preferably, the copolymers of thisinvention have about 5 to about 45 mole % unsaturation; more preferablyabout 5 to about 40 mole %; still more preferably about 8 to about 40and most preferably about 8 to about 30 mole %; e.g., 12 to about 30mole %.

The permeability of isobutylene-isoprene copolymers increasesexponentially with isoprene content--it decreases exponentially withcyclopentadiene content in isobutylene-cyclopentadiene copolymers--it isalmost additive for terpolymers of isobutylene-isoprene-cyclopentadiene.Thus, the effect of the addition of one unit of isoprene to theisobutylene chain can be counteracted by the effect of addition of oneunit of cyclopentadiene in the resultant impermeability value. Thus ifthe permeability of polyisobutylene (or the low isoprene unsaturates,i.e. the butyl rubbers) is found to be about 1×10⁻⁸ (cm² sec ⁻¹) undergiven test conditions it will remain unchanged atisoprene/cyclopentadiene levels of 5/5, 10/10, 20/20 etc. If the ratiois changed, e.g., to 10/20 then the permeability would resemble more thebehavior of the predominate structure (i.e. cyclopentadiene). Thereverse would hold for a ratio e.g. of 20/10.

Thus, the process of this invention permits the preparation of isoolefincopolymers and terpolymers, heretofore unattainable, which surprisinglyretain all the advantageous characteristics of conventional lowunsaturation butyl rubber while exhibiting improved vulcanizationcharacteristics and in some cases, e.g., cyclodiene containingcopolymers and terpolymers, improved ozone resistance and airimpermeability.

The term "substantially gel free" as used in the specification andclaims means copolymers containing less than 2 wt. % gel; morepreferably less than 1% gel, e.g., 1/2% gel. The term "D#" where # is aninteger means the volume % cyclopentadiene in a monomer mixture whereinD represents cyclopentadiene and the integer is the volume % diene.

DETAILED DESCRIPTION

The advantages of the physical properties of the compositions of thepresent invention can be more readily appreciated by reference to thefollowing examples and tables.

EXAMPLE I

The quantities of the reactants used in the preparations of thesecopolymers and terpolymers were measured as volumes at -78° C. and thevolumes converted to moles were needed using well certified densityvalues.

Monomer mixes comprising varying amounts of isobutylene and isoprene andin some experiments cyclopentadiene also, were polymerized in thepresence of an appropriate quantity of methylcyclohexane cosolvent. Thepolymerization was initiated using an 0.061M solution of ethylaluminumdichloride added at a rate such as to maintain the reactor temperaturewithin 2° of the indicated polymerization temperature. In some instancessmall quantities of an 0.031M solution of HCl were utilized wherein theHCl serves as a cocatalyst for the polymerization. All polymerizationswere conducted in a dry inert atmosphere. The reactors were carried outover about a 40 minute period at which time they were terminated by theaddition of a small quantity of 10% propanol in pentane. The reactorsolutions were then treated briefly with gaseous NH₃ and coagulated bypouring them into hot methanol containing an antioxidant. Polymersamples were dried in vacuo at about 60° C. Polymerization details arepresented in Table 1.

                                      TABLE I                                     __________________________________________________________________________    DETAILS OF POLYMERIZATION OF ISOBUTYLENE ISOPRENE                             COPOLYMERS AND TERPOLYMERS WITH CYCLOPENTADIENE                                                             Cat.                                                                             Co-Cat.      4129                                Isobutylene                                                                         Isoprene                                                                           Cyclopentadiene                                                                        Cosolvent                                                                           Sol'n                                                                            Sol'n    Yield                                                                             Notebook                        Sample                                                                            ml(mole)                                                                            ml(mole)                                                                           ml       ml    ml ml   T,C g   Numbers                         __________________________________________________________________________    1   2880(36.4)                                                                          320(3.72)                                                                          --       800   100                                                                              --   -110                                                                              243 22-110                          2   688(8.70)                                                                           112(1.30)                                                                          --       200    20                                                                              0.8  -110                                                                              49  117-4                           3   2720(34.4)                                                                          680(7.90)                                                                          --       600   200                                                                              --   -119                                                                              61  50-120                          4   654(8.27)                                                                           196(2.28)                                                                          --       100    35                                                                              2    -110                                                                              49  115-3                           5   621(7.85)                                                                           279(3.24)                                                                          --        50    50                                                                              2    -118                                                                              38  114-4                           6   2784(35.2)                                                                          320(3.72)                                                                           96(1.30)                                                                              800   200                                                                              --   -110                                                                              57  23-110                          7   2560(32.4)                                                                          480(5.58)                                                                          160(2.17)                                                                              800   200                                                                              8    -110                                                                              117 97                              __________________________________________________________________________     Cosolvent - methylcyclohexane                                                 Catalyst solution - 0.061M EtAlCl.sub.2 in methylcyclohexane                  Co-catalyst solution - 0.031 HCl in methylcyclohexane                    

EXAMPLE II

The polymers of Example I were formulated as follows:

    ______________________________________                                        Polymer:          100 parts by weight                                         ______________________________________                                        Zinc stearate     1.65                                                        HAF Carbon black  60                                                          Hydrocarbon oil plasticizer.sup.1                                                               20                                                          Antioxidant.sup.2 1.11                                                        Zinc oxide        5                                                           Sulfur            2.5                                                         Sulfenamide accelerator.sup.3                                                                   0.75                                                        ______________________________________                                         .sup.1 Flexon 845; ASTM Type 4                                                .sup.2 Thermoflex A; 50% N-phenyl-beta-naphthylamino; 25%                     p,p'dimethoxy-diphenyl amine; 25% diphenyl-p-phenylene diamne                 .sup.3 Santocure NS; N-tertiary butylbenzothiazole-2-sulfenamide.        

Samples were vulcanized at 336° F. to provide approximately equivalentcrosslink densities. The physical properties of the vulcanized samplesfrom Table 1 are presented in Table 2.

                                      TABLE II                                    __________________________________________________________________________    SOME PROPERTIES                                                               OF ISOBUTYLENE ISOPRENE COPOLYMERS AND TERPOLYMERS                            WITH CYCLOPENTADIENE AND THEIR VULCANIZATES.sup.(a)                           SEE ALSO TABLE I                                                                                         Tensile  4129                                      %        --Mn    Moduli, psi                                                                             Strength                                                                           %   Notebook                                  Sample                                                                            Unsat.sup.(b)                                                                      × 10.sup.-3(c)                                                               ν.sup.(d)                                                                     at 100%                                                                            at 300%                                                                            psi  Elong.                                                                            Numbers                                   __________________________________________________________________________    1   6.34 105  1.99                                                                             320   770 1465 565 65-5                                      2   10.6 91   1.77                                                                             365  1550 1810 355 119-4                                     3   16.8 114  1.72                                                                             235  1565 1985 365 67-6                                      4   18.6 88   1.90                                                                             465  --   1580 255 118-3                                     5   26.8 103  1.94                                                                             478  --   1960 280 116-4                                     6   7/17.sup.(e)                                                                       91   1.98                                                                             390  1740 2365 395 65-8                                      7   5/20.sup.(e)                                                                       91   1.82                                                                             340  1525 2160 415 155-1                                     __________________________________________________________________________     .sup.(a) Cured at 336° F. to approximately constant crosslink          density.                                                                      .sup.(b) Mole percent by infra-red technique.                                 .sup.(c) Membrane osmometry.                                                  .sup.(d) Crosslink density, moles/cm.sup.3  × 10.sup.-4.                .sup.(e) Isoprene/cyclopentadiene.                                       

Since many modifications and variations of this invention may be madewithout departing from the spirit or scope of the invention thereof, itis not intended to limit the spirit or scope thereof to the specificexamples thereof.

The practice of this invention can involve batch or continuouspolymerizations either isothermal or multi-temperature. Continuouspolymerization is preferred since it is more convenient for commercialoperation and gives more uniform (homogeneous) products. Molecularweight distributions (Mw/Mn) are preferably between 2.0 and 20.

What is claimed is:
 1. A substantially gel free copolymer consisting ofa major portion of one isoolefin having about 4 to 10 carbon atoms andabout 5 to about 45 mole % of conjugated diene having about 5 to about 9carbon atoms, said copolymer having an Mn from 90,000 to below 120,000,said one isoolefin being selected from the group consisting ofisobutylene, 2-methyl-1-butene, 3-methyl-1-butene or 4-methyl-1-pentene,and said one diene being selected from the group comprising isoprene,piperylene or methyl cyclopentadiene.
 2. The product of claim 1, whereinthe isoolefin is isobutylene and the diene is isoprene or piperylene,the diene content being about 8 to about 40 mole %.
 3. The product ofclaim 1, wherein the isoolefin is isobutylene and the diene ismethylcyclopentadiene, the diene content being about 8 to about 40 mole%.
 4. The product of claim 1, wherein the diene content is about 8 toabout 40 mole %.
 5. A substantially gel free terpolymer consisting of amajor portion of an isoolefin having about 4 to about 10 carbon atomsand a minor portion of an acyclic conjugated diene having about 5 toabout 9 carbon atoms and a cyclic conjugated diene having about 5 toabout 9 carbon atoms, a mole % unsaturation of said terpolymer being atleast about 8 mole % and an Mn of said terpolymer being from 90,000 tobelow 120,000, said isoolefin being selected from the group consistingof isobutylene, 2-methyl-1-butene, 3-methyl-1-butene or4-methyl-1-pentene, said acyclic diene being selected from the groupconsisting of isoprene or piperylene, and said cyclic conjugated dienebeing selected from the group consisting of cyclopentadiene andmethylcyclopentadiene.
 6. The product of claim 5, wherein said isoolefinis isobutylene, said acyclic diene is isoprene, and said conjugateddiene is cyclopentadiene.
 7. The product of claim 5, wherein said cyclicconjugated diene is cyclopentadiene.
 8. The product of claim 5, whereinsaid cyclic conjugated diene is methylcyclopentadiene.
 9. The product ofclaim 7, wherein said terpolymer contains at least about 8 mole %unsaturation.
 10. The product of claim 5, wherein said terpolymercontains at least about 8 mole % of said cyclic conjugated diene.